"Even though Microsoft has, in the past, made marketing capital from synchronising its releases, group product manager Ward Ralston says that the desktop and server groups are two separate units that do not need to be released simultaneously. Windows 7 will should make its official appearance this year, but that major shift in the desktop experience isn't going to be matched with a similar sea-change on the server Operating System front. Microsoft has settled for only a minor upgrade to Windows Server 2008."

Something to consider though is OS X and GNU/Linux distros are released much more frequently, and mostly incremental, evolutionary updates. It makes sense to release the client and server at the same time. Windows releases are often significantly different from their predecessors, and users need more time to adjust. By the time the server version of Windows is released, a large portion of workers already have the client at home, and are sufficiently familiar with it. This helps mitigate the burden of transition.

Besides, any enterprise that deploys software as soon as its released is downright foolish IMO, regardless of platform.